If you have diabetes, you’re probably already familiar with hemoglobin A1C. This measure, which requires a blood draw, is an estimate of your average blood sugar levels over the past several months.
While we have many diabetes numbers to think about, A1C tends to be the one that doctors care about most. That’s because most of the major studies evaluating long-term diabetes health have focused on A1C. When the health authorities design numerical targets for diabetes management success, they prefer A1C. It’s the most important biomarker of glycemic control.
A1C, when measured at your medical office or by a laboratory, is usually quite reliable. Except … when it isn’t.
There are a number of health situations, some of them fairly unusual, that can result in inaccurate A1C measurements. If your A1C seems like it doesn’t match your expectations, it might be wise to consult our list.
The most comprehensive treatment of the study that we found is a 2014 article by Michael Radin, MD, an endocrinologist who now works as an executive for Novo Nordisk. This work identifies a whopping 17 situations that may falsely lower or elevate an A1C measurement.
Some of these conditions are pretty obscure — this article will concentrate on the more common situations:
Anemia
Anemia, in which the body has too few red blood cells, causes your red blood cells to live longer. Longer blood cell life allows them to pick up more sugar, which will misleadingly increase A1C levels. This is the most common cause of false A1C results.
There are many different types and causes of anemia. You can become anemic if you don’t get enough iron, vitamin B12, or folate, among other nutrients, all of which are needed to produce red blood cells. The condition can be diagnosed with a blood test.
You Have an Unusual Hemoglobin Variant
There are many types of hemoglobin, the protein in red blood cells that carries oxygen. Something like 93 percent of people worldwide share the most common type of hemoglobin, which means about 7 percent have a less-common variant. While some A1C tests are designed to work with multiple hemoglobin variants, others are not, which can result in misleading measurements.
People with lineage from Africa, South and Southeast Asia, and the Mediterranean are more likely to carry one of these hemoglobin variants, and are therefore more likely to get misleading results from their A1C tests. For more details, check out this National Institutes of Health article on the topic: The A1C Test & Race/Ethnicity.
You Have Chronic Kidney Disease
Chronic kidney disease can result in uremia, which means that the kidneys are not clearing waste products as well as they should be. Dialysis treats uremia, but clinicians should know that it can make your A1C test results inaccurate.
You Recently Received a Blood Transfusion
A recent blood transfusion can push your A1C both up and down. Donor blood can have more or less glucose in it than your own, depending on the storage medium and the health of the donor.
You Use Pain Relievers
Two families of pain relievers are associated with an inaccurate A1C test:
Salicylates, such as aspirin (Bayer and others)
Opioids, such as hydrocodone (Vicodin) and oxycodone (OxyContin)
You Have Spleen Issues
The spleen removes old red blood cells from the circulatory system. Asplenia — in which the spleen is either absent or nonfunctional, as in sickle cell disease — leads to decreased red blood cell turnover and superficially higher A1C measurements.
You’re Older
A1C measurements increase as we age, even when our blood sugar control stays the same. A 2014 analysis found that A1C levels increase by nearly 0.1 percent per decade, in people both with and without diabetes.
You Take Vitamins C or E
Vitamin E, which reduces glycation (the attachment of sugar to red blood cells), may falsely decrease your A1C measurement. Vitamin C can falsely decrease or increase your A1C results, depending on the exact test used.
You’re Pregnant
The lifespan of the red blood cell drops during pregnancy, and more red blood cells are produced, which can result in artificially low A1C results. The change takes hold by about week 20 of gestation, and plateaus until the end of the pregnancy.
A1C and the Roller-Coaster Effect
A1C may be the gold standard for glycemic health, but it is not, by any means, perfect. One big flaw of A1C: It does not give us any information about glycemic variability, the blood sugar’s tendency to change. Two people with the same A1C level could experience very different measures of hypo- and hyperglycemia if one has reasonably steady blood sugar and the other is frequently on the “roller coaster.”
Why does it matter? Aside from the discomfort and danger of extreme blood sugar levels, the evidence also shows that glycemic variability may help cause diabetes-associated complications, especially vascular complications. While more good long-term research is required, most experts seem to believe that patients that experience more time out of range will suffer worse outcomes than those with steadier blood sugar, even at the same A1C level.
Continuous glucose monitors (CGMs) offer exquisite data on glycemic variability, especially the new time-in-range measurement.
Margin of Error
Don’t forget that even a lab-based A1C test has a margin of error, reportedly between 0.5 and 0.7 percent. Your A1C result will probably be within a few tenths of a point of your true A1C, but you can’t expect perfect precision.